The invention relates generally to the field of antennas, and more particularly, to slotted waveguide antennas.
A relatively large amount of research has been conducted on slotted, rectangular waveguide antennas and frequent reports have been made in the literature. For instance, see Johnson and Jasik, Antenna Engineering Handbook, 2ed., McGraw-Hill 1984, chapter 9, and S. Silver, Microwave Antenna Theory and Design, MIT Radiation Laboratory Series, pp. 287-301. Many of these antennas use probes to excite the slots. As is well known, probes have disadvantages including the potential for arcing at high power levels and difficulty in manufacture and assembly.
There has also been a moderate amount of research and reporting on slotted coaxial waveguide antennas operating in the fundamental TEM mode and on circular waveguides operating in the TM.sub.01 mode. See S. Silver, MIT Radiation Laboratory Series, Vol. 12, Microwave Antenna Theory and Design pp. 305-309, 325, and 328 and in Johnson and Jasik, Antenna Engineering Handbook, 2ed., pp. 28-15. These designs have fixed linear polarization and do not have azimuthal pattern control. Also see Cornbleet, "The Helical Slot Antenna," IEE Third International conference on Antennas and Propagation, ICAP 1983, Part I.
Prior coaxial line slot antennas typically operated in the TEM mode in coaxial line or in the TM.sub.01 mode in circular waveguide with the slots coupled by associated probes. The antenna had fixed transverse linear polarization. In these types of antennas, the slots are parallel to the longitudinal current flow lines of the TEM or TM.sub.01 modes, hence they would not radiate without probes that project into the waveguide.
Very little has been reported about slotted circular waveguide antennas without probe excitation except for long continuous slots to form a "leaky wave antenna" as reported in J. N. Hines, V. H. Rumsey, and C. H. Walter, "Traveling-Wave Slot Antennas," Proc. IRE, Vol. 41, 1953, p. 1629, FIG. 11. Also see J. S. Ajioka and G. M. Coleman, U.S. Pat. No. 2,818,565. A very wide, continuous longitudinal slot was used in circular waveguide and operation occurred in the TM.sub.01 mode. Narrow longitudinal slots would not radiate because they were parallel to the current flow lines (TM modes have longitudinal currents only). Very wide slots, where the width was on the order of the radius of the waveguide or wider, perturbed the guided wave enough to cause leakage from the waveguide.
All of the above-mentioned techniques have the disadvantage of fixed polarization transverse to the array. The discrete slot array technique has the further disadvantage of requiring the use of costly, high power limiting electric probes which are used to excite the slots. The continuous slot technique has the further disadvantage of radiation at neither broadside nor at endfire but at somewhere in between. The beam direction is generally determined by sin .theta.=.lambda./.lambda..sub.g.
Thus, it would be an advance in the art to provide an antenna which may radiate at relatively high power levels, which does not use coupling probes, which has controllable polarization, and which allows azimuthal pattern control.
In view of the above, it would also represent an advance in the art to provide a slotted circular or coaxial waveguide antenna having controllable polarization and azimuthal pattern control.
It is an object of the invention to provide a new and improved slotted, circular or coaxial waveguide antenna.
It is also an object of the invention to provide a circular or coaxial slotted waveguide antenna having controllable azimuthal patterns.
It is also an object of the invention to provide a slotted, circular or coaxial antenna that takes advantage of helical current flow lines for circumferential TE modes with circumferential variation greater than zero.
It is also an object of the invention to provide a slotted, circular or coaxial antenna which can provide beams from broadside to endfire with arbitrary or controllable polarization.